The present invention relates to a head drum construction of a spiral scanning-type videocassette recorder wherein a tape guide is formed at an outer peripheral surface of a lower drum to accurately guide a magnetic recording tape being travelled round a head drum. More particularly, the present invention relates to an improved tape guide construction of a head drum of a videocassette recorder comprising a V-shaped groove helically formed at an outer peripheral surface of a lower drum and a circular wire fixedly engaged with the entire length of said groove, which construction enables the machining thereof to be easy and precise.
In a generally-used videocassette recorder, a magnetic recording tape is tracked by a video head mounted on a head drum to record and reproduce an image signal, while being helically travelled round an outer peripheral surface of said rotating head drum. In order to prevent upward and downward movements of the tape from the helical travelling path on the head drum during the travel of the tape along said travelling path, there are guide posts adapted to restrain the upper edge of the tape, at inlet and outlet of the head drum, respectively. And also, a tape guide is inclinedly formed, with a certain helix angle, at the outer peripheral surface of the lower drum of the head drum to restrain the lower edge of the tape.
FIGS. 1 and 2A illustrate an example of conventional tape guide construction wherein a guide plate 2 having a certain guide angle .theta. and a certain thickness D' is fixed to an outer peripheral surface of a lower drum 1 by means of an adhesive or a fixing screw. Where the guide plate 2 does not adhere closely to the lower drum 1, thereby to form a gap therebetween, a tape T may engage in said gap, thereby causing the travel thereof to be rough and unstable. And also, it is difficult to accuratly set the desired guide angle .theta. in fixing the guide plate 2.
Another conventional construction is illustrated in FIG. 2B, wherein a tape guide 1a is integrally formed with a lower drum 1. In order to form the tape guide 1a, the lower drum 1 is chucked and rotated in a machining apparatus including a bite. As the bite is fed, the lower drum 1 is machined to form the tape guide 1a. In such machining work, the bite should be reciprocated about 200 times along a guide line, since the lead of the tape guide 1a is as long as about 10 mm. Such machining work should be also slowly carried out. As a result, a long machining time is needed, thereby causing the productivity to be poor.